Torque Converter Bolt Pattern - The 1947 - Present Chevrolet & GMC Truck Message Board Network

LT-102 · 11-07-2002, 06:54 PM

I want to install a higher stall torque converter in my 71' C20, with it's original TH350 transmission. I see there are apparently two different bolt patterns, small and large. I wanted to buy the converter before I pulled the transmission what size should it take. Or, could it be either one and I won't know until I pull the tranny?

crazy longhorn · 11-07-2002, 07:11 PM

The trucks have a 168 tooth flex plate(14" dia if stock). as a rule, this flex plate will take either converter (2 patterns). The 350t's as a rule have the small pattern,as do most aftermarket high stall converters......you should be in good shape.

**COBALT** · 11-07-2002, 07:21 PM

Well, you could do a little math and figure out what the bolt pattern is. Take your inspection plate off, and get a rough estimate of the diameterof your flex-plate. Then measure the distance between the edge of the flex plate to the weld nut on the converter for one weld nut. If one isn't visible you'll either have to turn the engine with the tranny in N, or have someone bounce the starter until one is visible.

Once you get that measurement assume your weld nut is probably something like 9/16" - 3/4" wide, and then subtract 1/2 of that + the measurement you made earlier from 1/2 of the diameter of the flex plate. That will tell you the distance from the center to the hole for the converter for one weld nut. There's three of them, so what you end up with is an equilateral triangle between all three mount points. That given the diameter of the flex plate, and the distance from the edge of the flex plate to the mounting holes is all you need.

crazy longhorn · 11-07-2002, 08:20 PM

you could count the teeth.....but that would make me insane(Im already crazy). Take a took at the starter, if the bolts are staggered, its a 168 T wheel(14" dia). If the bolts are straight across , it a 153 T wheel (12 3/4" dia"). just drop the inspct cover, & check if you have another set of holes in the flex plate that arent being used......

tom hand · 11-07-2002, 08:27 PM

Take a good look at your flexplate, a lot of them are drilled for both patterns

*Fast68Chevy* · 11-07-2002, 10:05 PM

you dont need to worry about patterns, both are in the wheel you have, youll be fine, go ahead and get the converter,

good luck

11-07-2002, 06:54 PM	#1
LT-102 Registered User Join Date: Nov 2000 Location: Greenville, Oh USA Posts: 166	Torque Converter Bolt Pattern I want to install a higher stall torque converter in my 71' C20, with it's original TH350 transmission. I see there are apparently two different bolt patterns, small and large. I wanted to buy the converter before I pulled the transmission what size should it take. Or, could it be either one and I won't know until I pull the tranny?

11-07-2002, 07:11 PM	#2
crazy longhorn Fabricate till you "puke" Join Date: Jun 2002 Location: Ill Posts: 9,402	The trucks have a 168 tooth flex plate(14" dia if stock). as a rule, this flex plate will take either converter (2 patterns). The 350t's as a rule have the small pattern,as do most aftermarket high stall converters......you should be in good shape. __________________ 69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears....

11-07-2002, 07:21 PM	#3
COBALT Senior Member Join Date: Sep 2001 Location: Seattle, WA, USA Posts: 5,817	Well, you could do a little math and figure out what the bolt pattern is. Take your inspection plate off, and get a rough estimate of the diameterof your flex-plate. Then measure the distance between the edge of the flex plate to the weld nut on the converter for one weld nut. If one isn't visible you'll either have to turn the engine with the tranny in N, or have someone bounce the starter until one is visible. Once you get that measurement assume your weld nut is probably something like 9/16" - 3/4" wide, and then subtract 1/2 of that + the measurement you made earlier from 1/2 of the diameter of the flex plate. That will tell you the distance from the center to the hole for the converter for one weld nut. There's three of them, so what you end up with is an equilateral triangle between all three mount points. That given the diameter of the flex plate, and the distance from the edge of the flex plate to the mounting holes is all you need. __________________ '69 3/4 ton C20 2wd-350ci/TH400 '69 3/4 ton Custom 20 2wd-350ci/4sp Manual '99 2wd 5.7 Chevy Tahoe Seattle, WA.

11-07-2002, 08:20 PM	#4
crazy longhorn Fabricate till you "puke" Join Date: Jun 2002 Location: Ill Posts: 9,402	you could count the teeth.....but that would make me insane(Im already crazy). Take a took at the starter, if the bolts are staggered, its a 168 T wheel(14" dia). If the bolts are straight across , it a 153 T wheel (12 3/4" dia"). just drop the inspct cover, & check if you have another set of holes in the flex plate that arent being used...... __________________ 69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears....

11-07-2002, 08:27 PM	#5
tom hand CCRider Join Date: Feb 2000 Location: Olive Branch,MS,USA Posts: 2,232	Take a good look at your flexplate, a lot of them are drilled for both patterns __________________ 72 GMC Sierra SWB almost finished---- 84 Softail Olive Branch MS

11-07-2002, 10:05 PM	#6
Fast68Chevy Account Suspended Join Date: May 2000 Location: IL Posts: 0	you dont need to worry about patterns, both are in the wheel you have, youll be fine, go ahead and get the converter, good luck



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